Aircraft Video Profile: SR-71 Interview of SR-71 Pilot

The Lockheed SR-71 “Blackbird” was an advanced, long-range, Mach 3+ strategic reconnaissance aircraft.[1] It was developed as a black project from theLockheed A-12 reconnaissance aircraft in the 1960s by Lockheed and its Skunk Works division. Clarence “Kelly” Johnson was responsible for many of the design’s innovative concepts. During reconnaissance missions, the SR-71 operated at high speeds and altitudes to allow it to outrace threats. If a surface-to-air missilelaunch was detected, the standard evasive action was simply to accelerate and outfly the missile.[2]

The SR-71 served with the U.S. Air Force from 1964 to 1998. A total of 32 aircraft were built; 12 were lost in accidents, but none lost to enemy action.[3][4] The SR-71 has been given several nicknames, including Blackbird and Habu.[5] Since 1976, it has held the world record for the fastest air-breathing manned aircraft, a record previously held by the YF-12.[6][7][8]

Development

Background

Lockheed’s previous reconnaissance aircraft was the relatively slow U-2, designed for the Central Intelligence Agency (CIA). The 1960 downing of Francis Gary Powers’s U-2 underscored the aircraft’s vulnerability and the need for faster reconnaissance aircraft. The CIA turned again to Kelly Johnson and Lockheed’s Skunk Works, who developed the A-12[9] and would go on to build upon its design concepts for the SR-71. The Flight Test Engineer in charge was Joseph F. Ware, Jr.[10][importance?]

The A-12 first flew at Groom Lake (Area 51), Nevada, on 25 April 1962. Thirteen were built; two variants were also developed, including three YF-12A interceptor prototypes, and two M-21 drone carrier variants. The aircraft was meant to be powered by the Pratt & Whitney J58 engine, but development ran over schedule, and it was equipped instead with the less powerful Pratt & Whitney J75. The J58s were retrofitted as they became available, and became the standard powerplant for all subsequent aircraft in the series (A-12, YF-12, M-21) as well as the SR-71. The A-12 flew missions over Vietnam and North Korea before its retirement in 1968. The program’s cancellation was announced on 28 December 1966,[11] due both to budget concerns[12] and because of the forthcoming SR-71.

SR-71

A-12 production on what would later become the Blackbird assembly line atSkunk Works

The SR-71 designator is a continuation of the pre-1962 bomber series; the last aircraft built using the series was the XB-70 Valkyrie; however, a bomber variant of the Blackbird was briefly given the B-71 designator, which was retained when the type was changed to SR-71.[13]

During the later period of its testing, the B-70 was proposed for a reconnaissance/strike role, with an RS-70 designation. When it was clear that the A-12 performance potential was much greater, the Air Force ordered a variant of the A-12 in December 1962.[14] Originally named R-12[N 1] by Lockheed, the Air Force version was longer and heavier than the A-12, with a longer fuselage to hold more fuel, two seats in the cockpit, and reshaped chines. Reconnaissance equipment included signals intelligence sensors, a side-looking radar and a photo camera.[14] The CIA’s A-12 was a better photo reconnaissance platform than the Air Force’s R-12, since the A-12 flew somewhat higher and faster,[12]and with only one pilot it had room to carry a superior camera[12] and more instruments.[15]

During the 1964 campaign, Republican presidential nominee Barry Goldwater repeatedly criticized President Lyndon B. Johnson and his administration for falling behind theSoviet Union in developing new weapons. Johnson decided to counter this criticism by revealing the existence of the YF-12A Air Force interceptor, which also served as cover for the still-secret A-12,[16] and the Air Force reconnaissance model since July 1964. Air Force Chief of Staff General Curtis LeMay preferred the SR (Strategic Reconnaissance) designation and wanted the RS-71 to be named SR-71. Before the July speech, LeMay lobbied to modify Johnson’s speech to read SR-71 instead of RS-71. The media transcript given to the press at the time still had the earlier RS-71 designation in places, creating the story that the president had misread the aircraft’s designation.[17][N 2]

In 1968, Secretary of Defense Robert McNamara canceled the F-12 interceptor program; the specialized tooling used to manufacture both the YF-12 and the SR-71 was also ordered destroyed.[18] Production of the SR-71 totaled 32 aircraft with 29 SR-71As, 2 SR-71Bs, and the single SR-71C.[19]

Design

Overview

The flight instrumentation of an SR-71’s cockpit

The SR-71 was designed for flight at over Mach 3 with a flight crew of two in tandem cockpits, with the pilot in the forward cockpit and the Reconnaissance Systems Officer (RSO) monitoring the surveillance systems and equipment from the rear cockpit.[20] The SR-71 was designed to minimize its radar cross-section, an early attempt at stealth design.[21] Finished aircraft were painted a dark blue, almost black, to increase the emission of internal heat and to act as camouflage against the night sky. The dark color led to the aircraft’s call sign “Blackbird”.

While the SR-71 carried electronic countermeasures to evade interception efforts, its greatest protection was its high speed and cruising altitude that made it almost invulnerable to the weapons of its day. Merely accelerating would typically be enough to evade a surface-to-air missile,[2] and the plane was faster than the Soviet Union’s principal interceptor, the MiG-25.[22] During its service life, no SR-71 was shot down.[3]

Airframe

On most aircraft, use of titanium was limited by the costs involved; it was generally used only in components exposed to the highest temperatures, such as exhaust fairings and the leading edges of wings. On the SR-71, titanium was used for 85% of the structure, with much of the rest polymer composite materials.[23] To control costs, Lockheed used a more easily worked alloy of titanium which softened at a lower temperature.[N 3] The challenges posed led Lockheed to develop new fabrication methods, and have since been used in the manufacture of other aircraft. Welding titanium requires distilled water, as the chlorine present in tap water is corrosive; cadmium-plated tools could not be used as they also caused corrosion.[24] Metallurgical contamination was another problem; at one point 80% of the delivered titanium for manufacture was rejected on these grounds.[25][26]

A Lockheed M-21 with D-21 drone on top

The high temperatures generated inflight required special design and operating techniques. Major portions of the skin of the inboard wings were corrugated, not smooth. (Aerodynamicists initially opposed the concept, disparaging referring the aircraft as a Mach 3 variant of the 1920s-era Ford Trimotor, known for its corrugated aluminum skin.[27]) The heat would have caused a smooth skin to split or curl, the corrugated skin could expand vertically and horizontally, it also increased longitudinal strength. Fuselage panels were manufactured to only loosely fit on the ground. Proper alignment was achieved as the airframe heated up and expanded several inches. Because of this, and the lack of a fuel sealing system that could handle the airframe’s expansion at extreme temperatures, the aircraft leaked JP-7 fuel on the ground. After takeoff, the aircraft would perform a short sprint to warm up the airframe, then refuel before heading to its destination.

Cooling was carried out by cycling fuel behind the titanium surfaces in the chines. On landing, the canopy temperature was over 300 °C (572 °F).[27] The red stripes on some SR-71s were to prevent maintenance workers from damaging the skin. Near the center of the fuselage, the curved skin was thin and delicate, with no support from the structural ribs, which were spaced several feet apart.[28]

Shape and threat avoidance

Water vapor is condensed by the low-pressure vortices generated by the chines outboard of each engine inlet.

The first operational aircraft designed around a stealthy shape and materials, the SR-71 had several features designed to reduce its radar signature. The SR-71 had a radar cross section (RCS) of around 10 square meters.[29] Drawing on early studies in radar stealth technology, which indicated that a shape with flattened, tapering sides would reflect most energy away from a radar beams’ place of origin, engineers added chines and canted the vertical control surfaces inward. Special radar-absorbing materials were incorporated into sawtooth-shaped sections of the aircraft’s skin. Cesium-based fuel additives were used to somewhat reduce exhaust plumes visibility to radar, although exhaust streams remained quite apparent. Kelly Johnson later conceded that Soviet radar technology advanced faster than the stealth technology employed against it.[30]

The SR-71 featured chines, a pair of sharp edges leading aft from either side of the nose along the fuselage. These were not a feature on the early A-3 design; Dr. Frank Rodgers of the Scientific Engineering Institute, a CIA front organization, discovered that a cross-section of a sphere had a greatly reduced radar reflection, and adapted a cylindrical-shaped fuselage by stretching out the sides of the fuselage.[31] After the advisory panel provisionally selected Convair’s FISH design over the A-3 on the basis of RCS, Lockheed adopted chines for its A-4 through A-6 designs.[32]

Aerodynamicists discovered that the chines generated powerful vortices and created additional lift, leading to unexpected aerodynamic performance improvements.[33] The angle of incidence of the delta wings could be reduced for greater stability and less drag at high speeds, and more weight carried, such as fuel. Landing speeds were also reduced, as the chines’ vortices created turbulent flow over the wings at high angles of attack, making it harder to stall. The chines also acted like leading-edge extensions, which increase the agility of fighters such as the F-5, F-16, F/A-18, MiG-29 and Su-27. The addition of chines also enabled the removal of the planned canard foreplanes.[N 4][34][35]

Air inlets

Operation of the air inlets and air flow patterns through the J58

The air inlets allowed the SR-71 to cruise at over Mach 3.2 while keeping airflow into the engines at the initial subsonic speeds. Mach 3.2 was the design point for the aircraft, its most efficient speed.[27] At the front of each inlet, a pointed, movable cone called a “spike” was locked in its full forward position on the ground and during subsonic flight. When the aircraft accelerated past Mach 1.6, an internal jackscrew moved the spike up to 26 inches (66 cm) inwards,[36] directed by an analog air inlet computer that took into account pitot-static, pitch, roll, yaw, and angle of attack. Moving the spike tip drew the shock wave riding on it closer to the inlet cowling until it touched just slightly inside the cowling lip. This position reflected the spike shock-wave repeatedly between the spike centerbody and the inlet inner cowl sides, and minimized airflow spillage which is the cause of spillage drag. The air slowed supersonically with a final plane shock wave at entry to the subsonic diffuser.[37]

Downstream of this “normal” shock wave the air is subsonic. It decelerates further in the divergent duct to give the required speed at entry to the compressor. Capture of the plane shock wave within the inlet is called “Starting the Inlet”. Bleed tubes and bypass doors were designed into the inlet and engine nacelles to handle some of this pressure and to position the final shock to allow the inlet to remain “started”. The SR-71 was sometimes more efficient at speeds higher than Mach 3.2 in terms of pounds of fuel burned per nautical mile traveled, depending on outside air temperature. During one mission, SR-71 pilot Brian Shul flew faster than usual to avoid multiple interception attempts; afterwards, it was discovered that this had reduced fuel consumption.[38]

In the early years of operation, the analog computers would not always keep up with rapidly changing flight environmental inputs. If internal pressures became too great and the spike was incorrectly positioned, the shock wave would suddenly blow out the front of the inlet, called an “Inlet Unstart”. During unstarts afterburner extinctions were common. The remaining engine’s asymmetrical thrust would cause the aircraft to yaw violently to one side. SAS, autopilot, and manual control inputs would fight the yawing, but often the extreme off-angle would reduce airflow in the opposite engine and stimulate “sympathetic stalls”. This generated a rapid counter-yawing, often coupled with loud “banging” noises, and a rough ride during which crews’ helmets would sometimes strike their cockpit canopies.[39] One response to a single unstart was unstarting both inlets to prevent yawing, then restarting them both.[40] Lockheed later installed an electronic control to detect unstart conditions and perform this reset action without pilot intervention.[41] Beginning in 1980, the analog inlet control system was replaced by a digital system, which reduced unstart instances.[42]

Engines

A Pratt & Whitney JT11D-20 engine on open display

A preserved AG330 start cart

The SR-71’s Pratt & Whitney JT11D-20 engine was a considerable innovation of the era; capable of producing a static thrust of 32,500 lbf (145 kN).[43] The engine was most efficient around Mach 3.2,[44] the Blackbird’s typical cruising speed. At lower speeds, the turbojet provided most of the compression. At higher speeds, the engine largely ceased to provide thrust, the afterburner taking its place.[43]

Air was initially compressed (and heated) by the inlet spike and subsequent converging duct between the centerbody and inlet cowl. The shock waves generated slowed the air to subsonic speeds relative to the engine. The air then entered the engine compressor. Some of this compressor flow (20% at cruise) was removed after the 4th compressor stage and went straight to the afterburner through six bypass tubes. Air passing through the turbojet was compressed further by the remaining 5 compressor stages and then fuel was added in the combustion chamber. After passing through the turbine the exhaust, together with the compressor bleed air, entered the afterburner.[45]

At around Mach 3, the temperature rise from the intake compression, added to the engine compressor temperature rise, reduced the allowable fuel flow because the turbine temperature limit did not change. The rotating machinery produced less power but still enough to run at 100% RPM, thus keeping the airflow through the intake constant. The rotating machinery had become a drag item[46] and the engine thrust at high speeds came from the afterburner temperature rise.[47] Maximum flight speed was limited by the air temperature entering the engine compressor at 800 °F (427 °C), which were not certified beyond that temperature.[48]

The Blackbird’s engines were originally started with the assistance of an external engine referred to as a “start cart”. The cart included two Buick Wildcat V8 engines positioned underneath the aircraft. The two engines powered a single, vertical driveshaft connecting to a single J58 engine. Once one engine was started, the cart was repositioned to start the other engine. Later, big-block Chevrolet engines were used. Eventually, a quieter, pneumatic start system was developed for use at main operating bases; the start carts remained at diversion landing sites not equipped to start J58 engines.[49]

Fuel

Several exotic fuels were investigated for the Blackbird. Development began on a coal slurry powerplant, but Johnson determined that the coal particles damaged important engine components.[27] Research was conducted on a liquid hydrogen powerplant, but the tanks for storing cryogenic hydrogen were not of a suitable size or shape.[27] In practice, the Blackbird would burn somewhat conventional JP-7 which was difficult to light. To start the engines, triethylborane (TEB), which ignites on contact with air, was injected to produce temperatures high enough to ignite the JP-7. The TEB produced a characteristic green flame, which could often be seen during engine ignition.[38]

The SR-71 required in-flight refueling to replenish fuel expended on take-off and during long duration missions. Supersonic flights generally lasted no more than 90 minutes before the pilot had to find a tanker.[50] To accomplish this, specialized KC-135Q tankers were required to refuel the SR-71. The KC-135Q had a modified high-speed boom, which would allow refueling of the Blackbird at nearly the tanker’s maximum airspeed, with minimum flutter; the tanker also had separate fuel systems to keep tanker’s fuel (either JP-4 or later JP-8) isolated from the JP-7 for the SR-71.[citation needed] As an aid to the pilot when refueling, the cockpit was fitted with a peripheral vision horizon display (PVHD). This unusual instrument displayed a barely-visible artificial horizon, which gave the pilot subliminal cues on aircraft attitude.[51]

Astro-Inertial Navigation System

The USAF sought a precision navigation system for maintaining route accuracy and target tracking at very high speeds.[citation needed] Nortronics, Northrop’s electronics development division, had developed an astro-inertial navigation system (ANS), which could correct navigation errors with celestial observations, for the SM-62 Snark missile, and a separate system for the ill-fated AGM-48 Skybolt missile, the latter of which was adapted for the SR-71.[52][verification needed]

Before takeoff, a primary alignment brought the ANS’s inertial components to a high degree of accuracy. In flight, the ANS, which sat behind the Reconnaissance Systems Officer (RSO)’s position, tracked stars through a circular quartz glass window on the upper fuselage.[38] Its “blue light” source star tracker, which could see stars during both day and night, would continuously track a variety of stars as the aircraft’s changing position brought them into view. The system’s digital computer ephemeris contained data on 56 (later 61) stars.[53] The ANS could supply altitude and position to flight controls and other systems, including the Mission Data Recorder, Auto-Nav steering to preset destination points, automatic pointing and control of cameras and sensors, and optical or SLR sighting of fix points loaded into the ANS before takeoff. According to Richard Graham, a former SR-71 pilot, the navigation system was good enough to limit drift to 1,000 feet off the direction of travel at Mach 3.[54]

Sensors and payloads

The SR-71 Defensive System B

The SR-71 originally included optical/infrared imagery systems; side-looking airborne radar (SLAR); electronic intelligence (ELINT) gathering systems; defensive systems for countering missile and airborne fighters; and recorders for SLAR, ELINT and maintenance data.[citation needed] The SR-71 carried a Fairchild tracking camera and an HRB Singerinfrared camera, both of which ran during the entire mission for route documentation, to respond to any accusations of overflight.[citation needed]

As the SR-71 had an observer behind the pilot, it could not use the A-12’s principal sensor, a single large-focal-length optical camera that sat in the “Q-Bay” behind the cockpit. Instead, camera systems could be located either in the wing chines or the interchangeable nose. Wide-area imaging was provided by two of Itek’s Operational Objective Cameras (OOCs), which provided stereo imagery across the width of the flight track, or an Itek Optical Bar Camera (OBC), which gave continuous horizon-to horizon coverage. A closer view of the target area was given by the HYCON Technical Objective Camera (TEOC), that could be directed up to 45 degrees left or right of the centerline.[55] Initially, the TEOCs could not match the resolution of the A-12’s larger camera, but rapid improvements in both the camera and film improved this performance.[55][56]

Side-looking radar, built by Goodyear Aerospace, could be carried in the removable nose. In later life, the radar was replaced by Loral’s Advanced Synthetic Aperture Radar System (ASARS-1). Both the first SLR and ASARS-1 were ground-mapping imaging systems, collecting data either in fixed swaths left or right of centerline or from a spot location for higher resolution.[55] ELINT-gathering systems, called the Electro Magnetic Reconnaissance System (EMR), built by AIL could be carried in the chine bays to analyse electronic signal fields being passed through, and were pre-programmed to identify items of interest.[55][57]

Over its operational life, the Blackbird carried various electronic countermeasures, including warning and active electronic systems built by several ECM companies and called Systems A, A2, A2C, B, C, C2, E, G, H and M. On a given mission, an aircraft would carry several of these frequency/purpose payloads to meet the expected threats.[citation needed] After landing, recording systems and gathered information from the SLR and ELINT systems, and the Maintenance Data Recorder (MDR) were subjected to post-flight ground analysis. In the later years of its operational life, a data-link system could send ASARS-1 and ELINT data from about 2,000 nmi (3,700 km) of track coverage to a suitably equipped ground station.[citation needed]

Life support

SR-71 pilot in full flight suit

Flying at 80,000 ft (24,000 m) meant that crews could not use standard masks, which could not provide enough oxygen above 43,000 ft (13,000 m). Specialized protective pressurized suits were produced by the David Clark Company for the A-12, YF-12, M-21 and SR-71. Furthermore, an emergency ejection at Mach 3.2 would subject crews to temperatures of about 450 °F (230 °C); thus, during a high altitude ejection scenario, an onboard oxygen supply would keep the suit pressurized during the descent.[citation needed]

The cockpit could be pressurized to an altitude of 10,000 or 26,000 ft (3,000 or 7,900 m) during flight.[58] The cabin needed a heavy-duty cooling system, for cruising at Mach 3.2 would heat the aircraft’s external surface well beyond 500 °F (260 °C)[59] and the inside of the windshield to 250 °F (120 °C). An air conditioner used a heat exchanger to dump heat from the cockpit into the fuel prior to combustion.[citation needed]

Operational history

An SR-71 refueling from a KC-135Q Stratotanker during a flight in 1983

The first flight of an SR-71 took place on 22 December 1964, at Air Force Plant 42 in Palmdale, California.[60] The SR-71 reportedly reached a top speed of Mach 3.4 during flight testing.[61][verification needed] The first SR-71 to enter service was delivered to the 4200th (later, 9th) Strategic Reconnaissance Wing at Beale Air Force Base, California, in January 1966.[62]

SR-71s first arrived at the 9th SRW’s Operating Location (OL-8) at Kadena Air Base, Okinawa on 8 March 1968.[63] These deployments were code named “Glowing Heat“, while the program as a whole was code named “Senior Crown“. Reconnaissance missions over North Vietnam were code named “Giant Scale“. On 21 March 1968, Major (later General) Jerome F. O’Malley and Major Edward D. Payne flew the first operational SR-71 sortie in SR-71 serial number 61-7976 from Kadena AB, Okinawa.[63] During its career, this aircraft (976) accumulated 2,981 flying hours and flew 942 total sorties (more than any other SR-71), including 257 operational missions, from Beale AFB; Palmdale, California; Kadena Air Base, Okinawa, Japan; and RAF Mildenhall, UK. The aircraft was flown to the National Museum of the United States Air Force near Dayton, Ohio in March 1990.

From the beginning of the Blackbird’s reconnaissance missions over enemy territory (North Vietnam, Laos, etc.) in 1968, the SR-71s averaged approximately one sortie a week for nearly two years. By 1970, the SR-71s were averaging two sorties per week, and by 1972, they were flying nearly one sortie every day. Two SR-71s were lost during these missions, one in 1970 and the second aircraft in 1972, both due to mechanical malfunctions.[64][65]

Early project Habu logo

While deployed in Okinawa, the SR-71s and their aircrew members gained the nickname Habu (as did the A-12s preceding them) after a pit viper indigenous to Japan, which the Okinawans thought the plane resembled.[5]

Swedish Air Force fighter pilots, using the predictable patterns of SR-71 routine flights over the Baltic Sea, managed to lock their radar on the SR-71 on numerous occasions. Despite heavy jamming from the SR-71, target illumination was maintained by feeding target location from ground-based radars to the fire-control computer in the JA 37 Viggen interceptor.[66] The most common site for the lock-on to occur was the thin stretch of international airspace between Öland and Gotland that the SR-71 used on the return flight.[67][68][69]

Operational highlights for the entire Blackbird family (YF-12, A-12, and SR-71) as of about 1990 included:[70]

3,551 Mission Sorties Flown

17,300 Total Sorties Flown

11,008 Mission Flight Hours

53,490 Total Flight Hours

2,752 hours Mach 3 Time (Missions)

11,675 hours Mach 3 Time (Total)

Only one crew member, Jim Zwayer, a Lockheed flight-test reconnaissance and navigation systems specialist, was killed in a flight accident.[71] The rest of the crew members ejected safely or evacuated their aircraft on the ground.

Initial retirement

In the 1970s, the SR-71 was placed under closer Congressional scrutiny and, with budget concerns, the program became a subject of criticism.[citation needed] Both Congress and the USAF sought to focus on newer projects like the B-1 Lancer and upgrades to the B-52 Stratofortress, whose replacement was being developed.[citation needed]

The SR-71 had never gathered significant supporters within the Air Force,[citation needed] making it an easy target for cost-conscious politicians. Dick Cheney told the Senate Appropriations Committee that the SR-71 cost $85,000 per hour to operate.[72] Opponents estimated a cost of $400 million per year to support the aircraft, this number was subsequently reduced to $260 million. As parts were no longer being manufactured, other airframes had to be cannibalized to keep the fleet airworthy. The lack of a datalink (unlike the Lockheed U-2) meant that imagery and radar data could not be used in real time, but had to wait until the aircraft returned to base. The Air Force saw the SR-71 as a bargaining chip which could be sacrificed to ensure the survival of other priorities. A general misunderstanding of the nature of aerial reconnaissance and a lack of knowledge about the SR-71 in particular (due to its secretive development and usage) was used by detractors to discredit the aircraft, with the assurance given that a replacement was under development. In 1988, Congress was convinced to allocate $160,000 to keep six SR-71s (along with a trainer model) in flyable storage that could become flightworthy within 60 days; however, the USAF refused to spend the money. While the SR-71 survived attempts to retire it in 1988, partly due to the unmatched ability to provide high-quality coverage of the Kola Peninsula for the US Navy,[73] the decision to retire the SR-71 from active duty came in 1989, with the last missions flown in October that year.[74] Four months after the plane’s retirement, General Norman Schwarzkopf, Jr., was told that the expedited reconnaissance, which the SR-71 could have provided, was unavailable during Operation Desert Storm.[75]

Reactivation

“From the operator’s perspective, what I need is something that will not give me just a spot in time but will give me a track of what is happening. When we are trying to find out if theSerbs are taking arms, moving tanks or artillery into Bosnia, we can get a picture of them stacked up on the Serbian side of the bridge. We do not know whether they then went on to move across that bridge. We need the [data] that a tactical, an SR-71, a U-2, or an unmanned vehicle of some sort, will give us, in addition to, not in replacement of, the ability of the satellites to go around and check not only that spot but a lot of other spots around the world for us. It is the integration of strategic and tactical.”

Response from Admiral Richard C. Macke to the Senate Committee on Armed Services.[76]

Due to unease over political situations in the Middle East and North Korea, the U.S. Congress re-examined the SR-71 beginning in 1993.[75] Rear AdmiralThomas F. Hall addressed the question of why the SR-71 was retired, saying it was under “the belief that, given the time delay associated with mounting a mission, conducting a reconnaissance, retrieving the data, processing it, and getting it out to a field commander, that you had a problem in timelines that was not going to meet the tactical requirements on the modern battlefield. And the determination was that if one could take advantage of technology and develop a system that could get that data back real time… that would be able to meet the unique requirements of the tactical commander.” Hall stated they were “looking at alternative means of doing [the job of the SR-71].”[76]

Macke told the committee that they were “flying U-2s, RC-135s, [and] other strategic and tactical assets” to collect information in some areas.[76] SenatorRobert Byrd and other Senators complained that the “better than” successor to the SR-71 had yet to be developed at the cost of the “good enough” serviceable aircraft. They maintained that, in a time of constrained military budgets, designing, building, and testing an aircraft with the same capabilities as the SR-71 would be impossible.[70]

Congress’ disappointment with the lack of a suitable replacement for the Blackbird was cited concerning whether to continue funding imaging sensors on the U-2. Congressional conferees stated the “experience with the SR-71 serves as a reminder of the pitfalls of failing to keep existing systems up-to-date and capable in the hope of acquiring other capabilities.”[70] It was agreed to add $100 million to the budget to return three SR-71s to service, but it was emphasized that this “would not prejudice support for long-endurance UAVs [such as the Global Hawk].” The funding was later cut to $72.5 million.[70] The Skunk Works was able to return the aircraft to service under budget at $72 million.[77]

Colonel Jay Murphy (USAF Retired) was made the Program Manager for Lockheed’s reactivation plans. Retired Air Force Colonels Don Emmons and Barry MacKean were put under government contract to remake the plane’s logistic and support structure. Still-active Air Force pilots and Reconnaissance Systems Officers (RSOs) who had worked with the aircraft were asked to volunteer to fly the reactivated planes. The aircraft was under the command and control of the 9th Reconnaissance Wing at Beale Air Force Base and flew out of a renovated hangar at Edwards Air Force Base. Modifications were made to provide a data-link with “near real-time” transmission of the Advanced Synthetic Aperture Radar’s imagery to sites on the ground.[70]

Final retirement

The reactivation met much resistance: the Air Force had not budgeted for the aircraft, and UAV developers worried that their programs would suffer if money was shifted to support the SR-71s. Also, with the allocation requiring yearly reaffirmation by Congress, long-term planning for the SR-71 was difficult.[70] In 1996, the Air Force claimed that specific funding had not been authorized, and moved to ground the program. Congress reauthorized the funds, but, in October 1997, President Bill Clinton attempted to use the line-item veto to cancel the $39 million allocated for the SR-71. In June 1998, the Supreme Court of the United States ruled that the line-item veto was unconstitutional. All this left the SR-71’s status uncertain until September 1998, when the Air Force called for the funds to be redistributed; the Air Force permanently retired it in 1998. NASAoperated the two last airworthy Blackbirds until 1999.[78] All other Blackbirds have been moved to museums except for the two SR-71s and a few D-21 drones retained by the NASA Dryden Flight Research Center.[77]

Timeline

24 December 1957: First J58 engine run.

1 May 1960: Francis Gary Powers is shot down in a Lockheed U-2 over the Soviet Union.

22 December 1964: First flight of the SR-71 with Lockheed test pilot Bob Gilliland at Air Force Plant #42.

21 July 1967: Jim Watkins and Dave Dempster fly first international sortie in SR-71A, AF Ser. No. 61-7972, when the Astro-Inertial Navigation System (ANS) fails on a training mission and they accidentally fly into Mexican airspace.

28 September 1994: Congress votes to allocate $100 million for reactivation of three SR-71s.

28 June 1995: First reactivated SR-71 returns to Air Force as Detachment 2.

9 October 1999: The last flight of the SR-71 (AF Ser. No. 61-7980/NASA 844).

Records

View from the cockpit at 73,000 feet (22,000 m) over the Atlantic Ocean.[79]

The SR-71 was the world’s fastest and highest-flying operational manned aircraft throughout its career. On 28 July 1976, SR-71 serial number 61-7962, broke the world record: an “absolute altitude record” of 85,069 feet (25,929 m).[8][80][81][82] Several aircraft have exceeded this altitude in zoom climbs, but not in sustained flight.[8] That same day SR-71, serial number 61-7958, set an absolute speed record of 1,905.81 knots (2,193.2 mph; 3,529.6 km/h), approximately Mach 3.3.[8][82]

The SR-71 also holds the “Speed Over a Recognized Course” record for flying from New York to London—distance 3,508 miles (5,646 km), 1,435.587 miles per hour (2,310.353 km/h), and an elapsed time of 1 hour 54 minutes and 56.4 seconds—set on 1 September 1974 while flown by U.S. Air Force Pilot Maj. James V. Sullivan and Maj. Noel F. Widdifield, reconnaissance systems officer (RSO).[83] This equates to an average velocity of about Mach 2.68, including deceleration for in-flight refueling. Peak speeds during this flight were likely closer to the declassified top speed of Mach 3.2+. For comparison, the best commercial Concorde flight time was 2 hours 52 minutes and the Boeing 747 averages 6 hours 15 minutes.

On 26 April 1971, 61-7968, flown by Majors Thomas B. Estes and Dewain C. Vick, flew over 15,000 miles (24,000 km) in 10 hrs. 30 min. This flight was awarded the 1971Mackay Trophy for the “most meritorious flight of the year” and the 1972 Harmon Trophy for “most outstanding international achievement in the art/science of aeronautics”.[84]

Pilot and RSO on 6 March 1990, the last SR-71 Senior Crown flight

When the SR-71 was retired in 1990, one Blackbird was flown from its birthplace at United States Air Force Plant 42 in Palmdale, California, to go on exhibit at what is now theSmithsonian Institution’s Steven F. Udvar-Hazy Center in Chantilly, Virginia.[85] On 6 March 1990, Lt. Col. Raymond E. “Ed” Yielding and Lt. Col. Joseph T. “JT” Vida piloted SR-71 S/N 61-7972 on its final Senior Crown flight and set four new speed records in the process.

Los Angeles, CA, to Washington, D.C., distance 2,299.7 miles (3,701.0 km), average speed 2,144.8 miles per hour (3,451.7 km/h), and an elapsed time of 64 minutes 20 seconds.[83]

West Coast to East Coast, distance 2,404 miles (3,869 km), average speed 2,124.5 miles per hour (3,419.1 km/h), and an elapsed time of 67 minutes 54 seconds.

Kansas City, Missouri, to Washington, D.C., distance 942 miles (1,516 km), average speed 2,176 miles per hour (3,502 km/h), and an elapsed time of 25 minutes 59 seconds.

St. Louis, Missouri, to Cincinnati, Ohio, distance 311.4 miles (501.1 km), average speed 2,189.9 miles per hour (3,524.3 km/h), and an elapsed time of 8 minutes 32 seconds.

These four speed records were accepted by the National Aeronautic Association (NAA), the recognized body for aviation records in the United States.[86] Additionally, Air & Space reported that the Air Force clocked the Blackbird at one point in its flight reaching 2,242.48 mph.[87] After the Los Angeles–Washington flight, Senator John Glenn addressed the United States Senate, chastening the Department of Defense for not using the SR-71 to its full potential:

Mr. President, the termination of the SR-71 was a grave mistake and could place our nation at a serious disadvantage in the event of a future crisis. Yesterday’s historic transcontinental flight was a sad memorial to our short-sighted policy in strategic aerial reconnaissance.

Successor

Speculation existed regarding a replacement for the SR-71, most notably a rumored aircraft codenamed Aurora. The limitations of satellites, which take up to 24 hours to arrive in the proper orbit to photograph a particular target, makes them slower to respond to demand than reconnaissance planes. The fly-over orbit of spy satellites may also be predicted and can allow assets to be hidden when the satellite is above, a drawback not shared by aircraft. Thus, there are doubts that the US has abandoned the concept of spy planes to complement reconnaissance satellites.[88] Unmanned aerial vehicles (UAVs) are also used for much aerial reconnaissance in the 21st century, being able to overfly hostile territory without putting human pilots at risk, as well as being smaller and harder to detect than man-carrying aircraft.

On 1 November 2013, media outlets reported that Skunk Works has been working on an unmanned reconnaissance airplane it has named SR-72, which would fly twice as fast at Mach 6.[89][90] However, the Air Force is officially pursuing the Northrop Grumman RQ-180 UAV to take up the SR-71’s strategic ISR role.[91]

Variants

SR-71A was the main production variant.

SR-71B was a trainer variant.[92]

SR-71C was a hybrid aircraft composed of the rear fuselage of the first YF-12A (S/N 60-6934) and the forward fuselage from an SR-71 static test unit. The YF-12 had been wrecked in a 1966 landing accident. This Blackbird was seemingly not quite straight and had a yaw at supersonic speeds.[93] It was nicknamed “The Bastard”.[94][95]

Accidents and aircraft disposition

SR-71 at Pima Air & Space Museum, Tucson, Arizona

Close-up of the SR-71B operated by NASA’s Dryden Flight Research Center,Edwards AFB, California

The SR-71A on display at the Boeing Aviation Hangar (Steven F. Udvar-Hazy Center).

SR-71A at the National Museum of the United States Air Force

Twelve SR-71s were lost and one pilot died in accidents during the aircraft’s service career.[3][4] Eleven of these accidents happened between 1966 and 1972.